1. Field of the Invention
The present invention relates to a dewatering apparatus of an automatic washing machine and a control method thereof, and more particularly, to a dewatering apparatus and the control method thereof in which an unbalance of a washing tub and an opening of a door can be accurately sensed to control them while performing a dewatering function after completing wash and rinse cycles in the washing machine.
2. Discussion of the Related Art
A conventional automatic washing machine is shown in FIG. 1 to FIG. 4. Since unbalance sensing switch 4a is mounted at one side of a top cover 1a on a body 16, switching points 24a,25a of first and second terminals 24,25 are coupled by upward movement of a door lever 22 and a switching lever 23 when a door 5a closes, to switch on current as shown in FIG. 2a.
As shown in FIG. 2a, if washing tub 3 oscillates during a dewatering process, the washing tub 3 bumps against an outer tub 15. At the same time, unbalance sensing lever 26 is deflected by a predetermined distance L by means of the outer tub 15. Likewise, the switching points 24a,25a of the first and second terminals 24,25 are isolated from each other by the action of switching lever 23 to switch off current as shown in FIG. 2b.
Laundry may lean to one side of the washing tub 3 while tub 3 spins to dewater the laundry, for dehydration after washing and rinsing. The washing tub 3 therefore becomes unbalanced thereby causing the washing tub 3 to bump against the outer tub 15. At the same time, the outer tub 15 pushes the unbalance sensing lever 26. As a result, the switching points 24a,25a of the first and second terminals 24,25 switch off for a certain time t.
Further, since the door lever 22 is not displaced when door 5a of the washing machine opens as shown in FIG. 2, the switching points 24a,25a of the first and second terminals 24,25 remain switched off until the door 5a closes.
Meanwhile, as shown in FIG. 3, a low signal is input to the microprocessor 21 when the unbalance sensing switch 4a is closed, while a high signal is input to the microprocessor 21 when the unbalance sensing switch 4a opens. Thus, when a signal having a predetermined level is input to the microprocessor 21 as shown in FIG. 4, an unbalance of the washing tub 3 is sensed when the signal input time is shorter than a certain the threshold time t of about 80-200 ms. The opening of the door 5a is sensed when the signal input time is longer than the threshold time.
However, since the opening of the door 5a and the unbalance of the washing tub 3 are simultaneously sensed by the unbalance sensing switch 4a as above, it is difficult to sense the opening of the door 5a when primarily on using the unbalance sensing switch 4a for sensing the unbalance of the washing tub 3. On the other hand, it is difficult to sense the unbalance of the washing tub 3 when primarily using the same for sensing the opening of the door 5a. In addition, the sensing performance depends on position of the unbalance sensing switch 4a.
Moreover, once the unbalance sensing switch is fixed to the washing machine, it is hard to change its configuration and position. If a relatively large amount of laundry is loaded into the washing tub 3, the position of the outer tub 15 is lower than a bottom portion of unbalance sensing lever 26 because of laundry's weight and a buffer force of a damper 27 mounted between a top portion of the body 16 and a bottom portion of the outer tub 15. This makes sensing the unbalance of the washing tub 3 impossible or causes deformation of the unbalance sensing lever 26 in case of its restoration as it is to occur malfunction of the sensing function of the unbalance. It is also likely for the unbalance sensing lever 26 protruding towards a lower portion of the top cover 1a to become deformed while transferring and assembling the top cover 1a, and while disassembling the machine for assembly and change of the washing machine.